Do I want a corridor or do I want an experience every time I walk in the door?” Daphne Guinness asked herself one recent afternoon.

Of course she wanted the experience.

So entering her new Fifth Avenue apartment, one proceeds through a hall that seems to stretch into infinity, thanks to its completely mirrored walls and ceiling. With bloodred carpet underfoot and a few striking works of contemporary art on view, including an enormous Damien Hirst butterfly painting, it’s a modern take on Versailles’s Galerie des Glaces meets carnival fun house.

“Some people get confused in there, but I love it,” says Guinness, taking a seat in her living room, which is pretty shiny as well—silver-leaf paper on the ceiling, high-gloss ebonized-wood floors, slightly smoky mirror on one wall.

Guinness herself sparkles, too. On a gray day, her arms are covered in antique diamond bracelets and a silver-lamé turban caps her signature skunk-streak hair. Fashion patron, muse, and model extraordinaire, she has grown accustomed to having her every move analyzed by designers, photographers, stylists, and editors. Given how often she’s photographed at glamorous events worldwide, it may be hard for some to believe she has a domestic life, let alone an intellectual side, but indeed she has both.

Scholarly books are stacked on nearly every table (close at hand are The Letters of Lord Byron; Christopher Marlowe: The Complete Plays; and Seneca: Six Tragedies). They are clearly not props; conversations with Guinness are anything but standard fashionista patter. Somehow particle physics comes up today. She is “mad,” she says, for the Large Hadron Collider, near Geneva, Switzerland. “All those atoms spinning around so fast—I’m obsessed with that.”

The daughter of an heir to the Irish brewing fortune (and granddaughter of one of the fabled Mitford sisters), Guinness grew up in stately homes in Ireland and England and spent summers in a 17th-century former hermitage on Spain’s Costa Brava, where Salvador Dalí and Man Ray were among the neighbors. In 1987, at age 19, she married Spyros Niarchos, son of the stratospherically wealthy Greek shipping tycoon Stavros Niarchos. For the next 12 years, life was a dizzying merry-go-round, as she shuttled between the family’s island and palatial homes on private planes and the clan’s superyacht, Atlantis II.

Following her divorce, it took a long while for Guinness to restore her equilibrium. “It was extremely destabilizing to me,” she recalls. “I had to put a lot of effort into recovering my balance.” A couple of years ago, she downsized from a mansion in London to an apartment there and began spending more time in New York. Eventually she chose a three-bedroom apartment—strictly on the basis of its high floor and its banks of north- and west-facing windows—in a grand building near the Metropolitan Museum of Art. “It’s all about the light,” she says. “North for drawing, west for sunsets.”

Though she had definite ideas about the decor, she wanted help executing them. Fortuitously the building manager suggested she meet Daniel Romualdez, the architect who was designing the apartment above hers, whose clients include Tory Burch and Aerin Lauder. Their meeting over tea at the Carlyle hotel turned from job interview to impassioned design session within minutes. “We started sketching right then,” Romualdez says.

As he would do many times during their subsequent meetings, Romualdez took decorative cues from his client’s personal style. “She was wearing a silver-lamé Chanel coatdress, so right away I knew there had to be silver,” he says. He also matched the scarlet carpet in the corridor to Guinness’s custom-blended nail polish.

“Daniel got all my references immediately,” she says. “I told him I wanted the shine of Metropolis, the modernity that should have happened,” she explains, “with the lush flora of Suddenly, Last Summer. But I didn’t want it to tip into English decadence. It had to be contained, controlled—intelligent decadence. What I wanted was sort of a savage modernism.”

“The minute she said Fritz Lang, I knew just what to do,” says Romualdez. “It was all very fast and easy, almost effortless. The only challenge was keeping up with her mind. Daphne is exploding with ideas.”

She gets many of them, it seems, while hanging out—literally—on an inversion table she keeps in her office. “I spend a lot of time upside down,” she says. “It increases the blood flow to the brain, so it really helps your creativity.”

Perhaps it was during one of her dips that Guinness came up with the idea of mirroring her entire bathroom. “It was sort of an homage to my mother, who had a mirrored bath in the country,” she says. Recently this space received unsolicited publicity (Heiress in Bath Lather, read a headline last fall in the New York Post). Following multiple overflows, Guinness’s downstairs neighbor had filed a lawsuit and attempted to take out an injunction barring her from bathing in it. “My infamous tub,” she moans when the subject comes up. “I’m mending it,” she adds.

In furnishing the apartment, Romualdez designed a number of upholstered pieces, among them a pair of plump white chaises and a matching sofa in the living room, while Guinness provided much of the remaining furniture herself—either from her previous home in London or from warehouses filled with stored antiques—including a long mahogany table by Jacques Adnet. “It had never fit into any of my houses, but it fits perfectly here,” she says.

She assembled all the art herself, including a collection of photographs by Irving Penn, Nobuyoshi Araki, Gregory Crewdson, Bert Stern, and, most prominently, David LaChapelle, who is one of her closest friends.

The place has found favor with her three children, 15, 19, and 21, who often come to stay between school terms (although, she laments, “They just want to be downtown when they are in New York”). Another frequent visitor is Bernard-Henri Lévy, the eminent and debonair French intellectual, who lives in Paris. The pair’s friendship has been the subject of much talk on both sides of the Atlantic. “He’s here a lot,” she says. “He likes the apartment.”

Even with a glittering new perch at her disposal, Guinness rarely stays in the same place for long. She is leaving early in the morning for a yoga and kite-surfing retreat in Mexico before she flies on to Miami and London. “I like change, but I also like the baselines in my life to be the same,” she notes. “It’s quite nice to have a place to leave things. You can be a permanent gypsy, but it’s nice to go home.”